Devil's Sight.

Magical darkness doesn't impede Zariel's darkvision.

Legendary Resistance (3/Day).

If Zariel fails a saving throw, she can choose to succeed instead.

Magic Resistance.

Zariel has advantage on saving throws against spells and other magical effects.

Regeneration.

Zariel regains 20 hit points at the start of her turn. If she takes radiant damage, this trait doesn't function at the start of her next turn. Zariel dies only if she starts her turn with 0 hit points and doesn't regenerate.

Actions

Multiattack.

Zariel makes three Flail or Longsword attacks. She can replace one attack with a use of Horrid Touch, if available.

Flail.

Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 17 (2d8 + 8) force damage plus 36 (8d8) fire damage.

Longsword.

Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 17 (2d8 + 8) radiant damage, or 19 (2d10 + 8) radiant damage when used with two hands, plus 36 (8d8) fire damage.

Horrid Touch (Recharge 5–6).

Zariel touches one creature within 10 feet of her. The target must succeed on a DC 26 Constitution saving throw or take 44 (8d10) necrotic damage and be poisoned for 1 minute. While poisoned in this way, the target is blinded and deafened. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Spellcasting.

Zariel casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 26):

At will: alter self (can become Medium when changing her appearance), detect evil and good, fireball, invisibility (self only), major image, wall of fire
3/day each: blade barrier, dispel evil and good, finger of death

Teleport.

Zariel teleports, along with any equipment she is wearing or carrying, up to 120 feet to an unoccupied space she can see.

Legendary Actions

Zariel can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Zariel regains spent legendary actions at the start of its turn.

Teleport. Zariel uses Teleport.
Immolating Gaze (Costs 2 Actions). Zariel turns her magical gaze toward one creature she can see within 120 feet of her and commands it to burn. The target must succeed on a DC 26 Wisdom saving throw or take 22 (4d10) fire damage.

Lair Actions

On initiative count 20 (losing initiative ties), Zariel can take one of the following lair actions; she can't take the same lair action two rounds in a row:

Fireball. Zariel casts the fireball spell.
Infernal Illusions. Zariel casts the major image spell four times, targeting different areas with it. Zariel prefers to create images of intruders' loved ones being burned alive. Zariel doesn't need to concentrate on the spells, which end on initiative count 20 of the next round. Each creature that can see these illusions must succeed on a DC 26 Wisdom saving throw or become frightened of the illusion for 1 minute. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Regional Effects

The region containing Zariel's lair is warped by her magic, which creates one or more of the following effects:

Hellscape. The area within 9 miles of the lair is filled with screaming voices and the stench of burning meat.
Pyres. Once every 60 feet within 1 mile of the lair, 10-foot-high gouts of flame rise from the ground. Any creature or object that touches the flame takes 7 (2d6 fire damage, though it can take this damage no more than once per round.
Smoke. The area within 2 miles of the lair, but no closer than 500 feet, is filled with smoke, which causes the area to be heavily obscured. The smoke can't be cleared away.

If Zariel dies, these effects fade over the course of 1d10 days.